HVAC systems are typically provided on motorized vehicles such as trucks, busses, motor homes, etc. and vessels such as boats, ships, etc. (hereinafter collectively referred to as “mobile units”). During operation of the mobile unit the HVAC system is powered by the energy produced by the mobile unit's engine(s). The HVAC system, however, cannot operate during periods when the mobile unit is not in operation and the engine is turned off. Thus, while the operator of the mobile unit is resting he or she has the choice of either letting the engine idle in order to run the HVAC system and maintain a comfortable environment inside the mobile unit or turn off the engine and rest in a less than desirable environment. Regarding the former choice, idling the engine to maintain a comfortable environment for the operator is not desired for several reasons. For example, idling the engine during rest periods increases the operating costs of the mobile unit, increases the wear and tear on the engine and associated components, increases undesirable emissions, etc. Regarding the latter choice, the operator may not be able to achieve optimum rest due to extreme temperatures, thus, increasing the safety risk during operation of the mobile unit. There are circumstances where there are independent-external power sources available to allow the operator to power the HVAC system without idling the engine. These external power sources, however, are not always available. Thus, what is required is an HVAC system that can operate with or without the idling of the mobile unit's engine.
HVAC systems for mobile units that can operate with or without the mobile unit's the idling of the mobile unit's engine are generally known. Further, DC-powered HVAC systems are also generally known. Increasing the efficiency and maximizing the operating capacity of the DC-power, however, remains an interest in improvements in these systems. These improvements can be realized by utilizing variable-speed components such as a variable-speed compressor, a variable-speed condenser fan and a variable-speed evaporator fan. Thus, what is required is variable-speed-DC-powered HVAC system.